1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital camera or a video camera, using an image pickup element, and to a zoom lens that can be used with an image pickup apparatus.
2. Description of the Related Art
In recent years, image pickup apparatuses, such as digital cameras or video cameras, using an image pickup element for forming an image have required compactness of the entire image pickup apparatus and high quality of the formed image.
It has been desired that image pickup apparatuses, for example, digital cameras, should be compact which leads to portability for users and which are anteroposteriorly thin.
Some zoom lens barrels have been known, which utilize a retractable lens structure (collapsible mount type structure) having high accommodation efficiency so as to reduce the thickness of a camera.
U.S. Pat. No. 6,771,432 discusses a variable magnification image taking device, in which an image pickup element is moved to follow an image forming position, which varies during zooming.
Japanese Patent Application Laid-Open No. 2004-37967 and U.S. Pat. No. 6,771,432 discuss thin cameras (image pickup apparatuses) employing an optical-path-bending optical system, in which a reflecting member is located to deflect an optical axis or path substantially 90°, thus reducing an optical thickness of the optical system in the direction of an object side (i.e., an anteroposterior direction of the optical system).
Japanese Patent Application Laid-Open Nos. 2005-84151 and 2006-106071 discuss zoom lenses employing an optical-path-bending zoom optical system, in which an image pickup element is moved along an optical axis during zooming, thus miniaturizing the entire optical system.
Appropriate setting of conditions for moving each of lens units and an image pickup element in a zoom lens is needed to compensate for movement of an image plane caused by the variation of magnification and to simplify a moving mechanism for moving the lens units during zooming.
However, the number of moving mechanisms is increased in a case where an image pickup element is moved independent of lens units in a thin-shaped optical-path-bending zoom lens (or zoom lens system) in which a reflecting member is located on an optical path of the optical system and an optical axis thereof is bent by the reflecting member to reduce a thickness in an anteroposterior direction of the image pickup apparatus. Further, the moving mechanisms become complex and large.
In order to maintain high optical performance and to reduce the thickness in the anteroposterior direction of the image pickup apparatus, it is useful to locate a reflecting member for bending an optical axis at an appropriate position on an optical path of an optical system and to appropriately select lens units that are movable during zooming.
If conditions for moving a lens unit, which includes the reflecting member, and the image pickup element are not appropriately set in the optical-path-bending zoom optical system, it is difficult to obtain a high variable-magnification zoom optical system having a wide field angle.